Nor-Lake Plasma Freezers & Blood Bank Refrigerators - Manual (Page 5)

5
OPERATION
The plasma freezers and blood bank refrigerators employ a unit cooler evaporator located inside
the cabinet as the heat-removing source. Through the refrigeration process, heat is captured in the
evaporator, transferred to the condensing unit on top of the cabinet, and expelled to the surrounding
outside air. It is extremely important to allow a four-inch clearance on the top, rear, and sides of the
unit for the refrigeration process to function properly.
These refrigerators and freezers utilize a programmable controller to control the temperature and
defrost settings. The controller, which is located on the facade of the unit, is factory set. Please see
the separate default settings sheet and instructions on the operation of the controller used in the
Plasma Freezers. See the separate instructions on the operation of the controller used in the Blood
Bank Refrigerators.
Note: These cabinets are equipped with two switches located on the façade. One is the main power
ON/OFF switch for the unit. The other is a three-position switch for the battery-powered alarm. The
alarm switch is placed in the middle, or OFF position, for shipment. When the cabinet is put into
operation, the top of the switch should be pushed in to the ON position. With the switch in the ON
position, the battery will sound the alarm if the main power to the cabinet is interrupted. The switch
flipped to the bottom position is used to test the battery. This test must be done with power
uninterrupted to the cabinet. The alarm will sound if the battery is good. This test should be done
periodically. The battery is located inside the control box that is on top of the unit behind the façade.
CAUTION: Disconnect the power to the cabinet when going into the control box to replace
the battery.
REFRIGERATORS
During the operation of a refrigerator, frost will periodically form on the coil surface. Each time the
compressor cycles "off", the evaporator fans will continue to run, which will keep the internal
temperature uniform and at the same time remove any frost build up on the coil. The water
produced will collect in the unit cooler drain pan and travel down the drain tube to the condensate
vaporizer.
FREEZERS
After shutting the door on freezer models, a short amount of time must be allowed before the door
can be reopened. This is due to the tight seal maintained between the door and the cabinet. Waiting
a few moments for the pressure to equalize permits the door to be opened easily.
A positive defrost is required to remove frost from the coil in freezer models. This is accomplished
by energizing heaters during the defrost cycle that are positioned on the coil surface. The
programmable controller is factory set to allow four defrosts per day.
As the preset defrost time is reached, the controller automatically terminates the refrigeration
process by turning off the condensing unit and unit cooler fan motors, and energizes the defrost
heaters. As the coil temperature increases, the frost begins to melt producing water that runs down
the coil to the unit cooler drain pan and exits through the drain tube to the vaporizer. After all the
frost has been removed and the coil temperature reaches approximately
10˚C , defrost is terminated
through the action of the defrost termination control located on the unit cooler, and the refrigeration
process resumes. In order to insure that any excess water remaining on the coil is not sprayed into
the cabinet interior, and all heat generated by the defrost is removed, the unit cooler fans will not
operate until the coil temperature reaches approximately
-10˚C .